Collapsible reservoir



Oct. 10, 1961 P. M. MILLER 3,003,659

COLLAPSIBLE RESERVOIR Filed Sept. 11, 1958 FIG. I

INVENTOR.

PRENTICE M. MILLER United States Patent f 3,003,659 COLLAPSIBLERESERVOIR Prentice M. Miller, Battle Creek, Mich., assignor to ClarkEquipment Company, a corporation of Michigan Filed Sept. 11, 1958, Ser.No. 760,396 1 Claim. (Cl. 220-85) This invention relates to reservoirsand more especially to collapsible reservoirs particularly adapted foruse in hydraulic systems.

Frequently, indoor industrial vehicles, such as industrial lift trucks,are required to operate in manufacturing areas wherein a corrosive,highly dust laden, or otherwise contaminated atmosphere is present.Heretofore, exended use of such vehicles in contaminated atmospheres hasoften resulted in damage to parts of the vhicles hydraulic system.Hydraulic systems for industrial lift trucks usually include in a closedcircuit an oil reservoirs, one or more hydraulic pumps, and varioushydraulic motors such as a piston and cylinder assembly for lifting aload on an upright mast located adjacent one end of the vehicle andothers for tilting the mast. The oil reservoir of such a system hasheretofore been vented to the atmosphere so that atmospheric pressure ismaintained above the surface of the hydraulic oil in the reservoirirrespective of variations in the volume thereof which, of course,varies from a maximum to a minimum depending upon whether one or morehydraulic devices in the circuit are in operation. With such anarrangement air from the atmosphere is drawn into the reservoir as thevolume of liquid therein decreases.

In an atmosphere which is contaminated by corrosive elements, eventualdamage to the hydraulic devices through which the hydraulic fluid flowswill usually be caused as a result of absorption of such elements by thehydraulic fluid.

I have devised a simple but extremely effective construction, by meansof which such harmful result is avoided. According to this invention Iprovide an expansible and contractible bladder element which is sealinlyconnected with the reservoir of such an hydraulic system. The bladderelement is located to communicate with the air space above the liquidcontained in the reservoir so that the bladder automatically contractsand expands as the liquid level lowers and rises, respectively.

It is an important object of this invention to provide a collapsiblecontainer connected to a reservoir in an hydraulic system for thepurpose of maintaining adequate gas pressure above the liquid level inthe reservoir while sealing the reservoir from communication with thesurrounding atmosphere.

It is another object of this invention to seal a liquid reservoir fromcommunication with the surrounding atmosphere while providing meansassociated with the reservoir for minimizing variations in pressure inthe air space of the reservoir with variations in the volume of liquidcontained therein.

Referring now to the drawing, a liquid reservoir is represented by thenumeral 10, the liquid therein by the numeral 12, and the air spacethereof by the numeral 14. A pump 16 communicates with the liquid 12through the suction pipe 18 and a filter 20 for pumping pressurizedfluid to one or more hydraulic devices, not shown, connected between apressure discharge conduit 22 and a low pressure return line 24. Line 24is connected to a 3,003,659 Patented Oct. 10, 1961 conduit 26 whichconducts low pressure return liquid back to the reservoir 10.

A frame or screen 28 extends upwardly from the reservoir and isconnected to the upper surface thereof. Within the frame 28 is mounted aflexible bladder member 30, which may be of rubber or plastic, forexample, the bladder having an open section 32 therein which is securedin sealed relation with a cylindrical wall 36 by means of a ring 34. Thewall 36 forms an aperture 38 in the upper Wall of the reservoir 10,whereby the space internal of bladder member 30 is in continuous andfree communication with air space 14. A valvular means 40 is connectedto bladder 30, and may, for instance, be of the type used with theinner-tubular members of tires and the like. Valvular means 40 may beused to control the gas or air pressure internal of bladder 30 at anygiven ambient temperature and pressure con dition and when the liquid 12fills the reservoir to a given level.

In operation the bladder 30 will collapse as the level of liquid 12 islowered during operation of pump 16 and will expand as the liquid levelis raised. Preferably, the bladder element should be capable ofsufl'icient change in volume to maintain substantially constant thepressure in space 14 during a change in volume of the liquid in thereservoir between maximum and minimum.

Although the construction of my device is simple, which in itself is avirtue, it solves a long standing problem by aflording a reservoir forhydraulic systems which is sealed from communication with surroundingcontaminated atmosphere and in which the air or gas space tends toremain at a relatively fixed pressure despite variations in the level ofliquid therein.

'11: will also be readily apparent to persons skilled in the art that asecond beneficial result may be realized by my construction if thebladder element is initially pressurized an amount which issubstantially equal to or somewhat greater than the suction head of thepump 16. The result of such pressurization has the effect ofneutralizing the suction head of the pump; i.e., allowing the suctionside of the pump to operate at a zero or positive gage pressure ratherthan at a negative gage pressure, thus eflecting an increase in pumpefl'iciency.

Although only one embodiment of the invention has been illustrated anddescribed, various changes in the form and relative arrangement of theparts may be made to suit requirements.

I claim:

A hydraulic supply system for vehicles operating in contaminatedatmosphere comprising a closed rigid reservoir containing sealed fromthe surrounding atmosphere and containing hydraulic fluid, a gaseousfluid contained in the space of the reservoir above the level of thehydraulic fluid, a flexible bladder-like reservoir containing suchgaseous fluid and adapted to expand and contract its volume to minimizevariations in pressure therein under certain conditions, a rigid passageconnected to the rigid reservoir and extending into the flexiblereservoir for continuously communicating the gaseous fluid in theflexible reservoir with the gaseous fluid in the rigid reservoir, saidflexible reservoir having a flexible opening for receiving said rigidpasage, said opening being formed of an annular loop, a sealing ringreceived in said annular loop for sealing said flexible opening withrespect to said rigid passage, variations in the level of hydraulicgaseous fluid pressure in the supply system is maintained while saidsystem is sealed from contamination by the atmosphere.

References Cited in the file of this patent UNITED STATES PATENTSBessesen Oct. 16, 1923 Perry Dec. 13, 1927 Johnson Oct. 30, 1928 KindlMar. 28, 1939 Knauth July 21, 1942 Johnson Apr. 18, 1944 Shriro Aug. 13,1946 Amidon Sept. 1, 1953 Fletcher Oct. 12, 1954 UNITED STATES PATENTOFFICE CERTIFICATION OF CORRECTION Patent No. 3,003,659 October 1O 1961Prentice M. Mil 'ler It is h'ereby certified that error appears in theabove numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column l',fl.lines 18 and 19 for "reservoirs" read reservoir column 2,line 51, strike out "containing.,

Signed and sealed this 3rd day of April 1962.

(SEAL) Attest:

ERNEST W. SWIDER I DAVID L. LADD Attesting Officer Commissioner ofPatents

